In rotating anode type X-ray tubes it is necessary to locate the anode target axially relative to the electron beam impinging thereon to obtain the necessary focal spot stability. One present type of rotating anode tube utilizes an anode structure, normally of tungsten, which anode is quite massive and supported in cantilever configuration. Other such rotating anode tubes may have a rotating anode wherein both ends of the anode structure are supported by bearing means such as shown in U.S. Pat. No. 4,545,064.
In prior art devices, a high intensity electron beam is directed through a vacuum at the tungsten anode target which converts the electron beam to X-rays which are then bounced off of the anode and directed outwardly through a filtering window onto the subject. The electron beam is of a very high intensity such that if the tungsten target is not rotated, the beam evaporates material on the target or burns the target. Accordingly, the tungsten anode (target) must be driven to rotate at a high speed to dissipate the heat. Powerful starters drive the anode target from an initial stop condition to 10,000 rpm in a fraction of a second before the exposure is made and stop the anode target in a short time after the exposure.